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Generalised overview of southern Swedish bedrock geology. Bedrock geology is generalised to the categories presented in Table 1. Bedrock data is derived from SGU 1:250 000 and 1:500 000 maps.
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This thesis investigates stream-lined subglacial bedforms (often referred to as drumlins) in southern Sweden. The broad aim of this is to contribute to the solution of the ‘drumlin problem’. The term drumlin has come to be applied to a wide range of features whose internal architecture (core) and overall morphology are seen to vary greatly. This ra...
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... and acidic volcanic rocks from the Transscandinavian Granite-Porphyry belt. The western part of the study area is formed of the granite and the orthogneiss of SW Sweden. The southernmost sec- tion of the study area, SW Skåne, consists of Phanerozoic limestone, shales, and sandstones. For a more detailed breakdown of the bedrock geology see Fig. 9. The various rock types are grouped together into eight simplified cat- egories which are presented in Table ...
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... drumlinoids are located. These were: (i) bedrock mapping from the Swedish Geological Sur- vey (SGU), (ii) Quaternary unit mapping from the SGU, (iii) the SGU drift depth model and (iv) well log records for the Hackvad area. Again all data is delivered georef- erenced to SWEREF TM99; all maps were delivered in polygon format. The bedrock mapping ( Fig. 9) used in the self-organising map (SOM) analysis (paper III) is a rasterised composite of 1:250 000 maps where available and 1:500 000 maps to fill the gaps in the higher resolu- tion coverage. The quaternary maps used in the mapping procedure described below is at a scale of 1:50 000. The SGU drift depth model is generated from a ...
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... similarity plot for Ireland (Fig. 9, panel B) is compli- cated by the presence of two categorical variables. 'Length' is seen to not be particularly closely associated with any of the contextual variables, the closest being 'Lim' and 'FeV', followed by an assortment of the other crystalline rock categories. However, the division of drift depth into specific groups ...
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... eastern Småland (Fig. 1), is another larger agglomeration of ribbed moraine ridges (some 530 ridges), demonstrating a strong NE -SW lineation which is perpendicular to the , NW -SE ice-flow direction at deglaciation across this eastern part of Småland (Persson 2010). A smaller portion of this ribbed moraine area is illustrated in the DEM scene of Fig. 5 (frame 9 in Fig. 1C). The strong lineation is formed from larger moraine ridges, usually in the dimensions 200 -300 m long, 100-150 m wide and a mean area per feature of 2386 m 2 . The height P 90 is at 10.6 m and the height P 10 at 3.3 m (Table 2). However, the DEM also reveals patches of hummocky moraine or single/few moraine hum- mocks, distributed in ...
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... hummocky moraine in this area (frame 1 in Fig. 1B; Fig. 9) has a height P 90 value of 3.6 m and a P 10 of 0.9 m, with a mean ER of 1.6 (mean width/length 31-51 m) ( Table 2). The hummocks occur in an irregular, i.e. uncontrolled and patchy distribution, leaving larger boggy depressions between more dense agglomerations of hummocks. A few streamlined terrain ridges with NE -SW trends can be ...
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... agglomerations and the location of features on streamlined terrain. Therefore the extracted morphometrics for this area must be considered a good estimate rather than an absolute truth. Andersson (1998) trenched three hummocks in the Lidhult area of which two sites, the Kvarnfallet and Sällebråten section, are situated within the DEM scene in Fig. 9. The c. 5-m-high sections showed stacked sequences of matrix-supported, massive sandy gravelly diamicts, interbedded with numerous thin beds of massive to laminated silty sand, some beds showing a slightly undulating configuration, some small-scale folding and varying inclinations in lateral directions. The frequency of sorted sediment ...
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... small sand pit in a ravine cut into the western flank of the area ,2 km NW of Rydaholm was re-excavated (R in Fig. 18), exposing 5.3 m of sorted sediment beneath a 1.7 -m-thick diamict (Fig. 19). The site is close to one of the drilled wells, here stating a total sediment thickness of 24 m above bedrock. All beds within the sorted sediment succession plunge ,188 towards the WSW (Fig. 19). The sediments predominantly consist of parallel-laminated medium to fine sand, some with floating outsized clasts (usually 3 -15 cm; MPS 30 ...
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... the western flank of the area ,2 km NW of Rydaholm was re-excavated (R in Fig. 18), exposing 5.3 m of sorted sediment beneath a 1.7 -m-thick diamict (Fig. 19). The site is close to one of the drilled wells, here stating a total sediment thickness of 24 m above bedrock. All beds within the sorted sediment succession plunge ,188 towards the WSW (Fig. 19). The sediments predominantly consist of parallel-laminated medium to fine sand, some with floating outsized clasts (usually 3 -15 cm; MPS 30 cm), interbedded with thicker units (10 -40 cm) of massive gravelly sand, also with the same kind of outsize clasts, the latter increasing in frequency upwards in the sequence. The lower part of ...
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... sequence. The lower part of the succession reveals a few coarse silt interbeds 2 -10 cm thick. This part is also vertically dislocated by 1.3 m along five normal faults. In one of these the sediments are dislocated by 90 cm, along which a 10-cm-thick shear zone has developed with lamination parallel to the enclosing fault planes (as indicated in Fig. 19). The smaller block faults clearly suggest that this faulting is synsedimentary because the fault planes are Fig. 16. Logs of sedimentary units and sediment facies in from trenches cut into the Grimslöv-Ströby drumlin (Fig. 15). Lithofacies codes according to Table1. Green planes in stereonet indicate strike and dip directions of ...
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... Rymmen is due to large frequency of outcropping bedrock with some till around them, forming rock-cored drumlins. Note the NW limit of the streamlined terrain (marked by white arrows). This boundary cuts obliquely through the streamlined terrain and gives an impression of late stage erosion on the stoss side of the area. Excavated site Rydaholm (Fig. 19) is marked by white circle. Hill shade constructed from LiDAR scan data provided by Lantmäteriverket, Sweden; q Lantmäteriverket ...
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... with meltwater transported sediments under different flow regimes, and with repeated cavity closure/ opening events, explaining the synsedimentary deformation of the sediments. This might very well be the type of sediment to expect in the drumlin lee-side tails of our study area, but only large-scale trenching would be able to confirm this. Fig. 19. Log of sedimentary units and sediment facies, as exposed in a cleaned-up ravine section within the western part of the patch of streamlined terrain between Lake Rymmen and Rydaholm (Fig. 18). Lithofacies codes according to Table 1. OSL ages according to ...
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... (insert in panel C, Fig. 20). These could later, after incremental stagnation, melt out in situ forming "A ˚ snen-type" ribbed moraine (Möller 2010) (see below). However, the DEM scene from the Lake Bolmen area with ribbed moraine draped on top of drumlin ridges (Fig. 4), and also partly hummocky moraine draping remnants of streamlined landforms (Fig. 9), suggest that the adfreezing processes within PZ-B were not that GFF 00 (2015) Möller and Dowling: Thermal boundary transitions and glacial geomorphology 27 pervasive here in this more westerly location, as compared to the Lake A ˚ snen area. During backwards migration of PZ-B into PZ- A the streamlined terrain of the latter zone was ...
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... lithological analysis of the gravel grade ( Fig. 19; H1- H4) shows in three samples a 100% clay-shale compo- sition. In a fourth sample the clay-shale was accompa- nied with small percentages (together ~7%) of crystalline rocks, sandstone and ...
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... Subglacial bedform genesis is a difficult process to study, both mathematically (Fannon et al., 2017;Fowler, 2018) and conceptually (Clark, 2010;Dowling, 2016). Clearly, numerous complex interactions are involved, and the 'drumlin problem' (as the formation of subglacial bedforms is often referred to) is compounded by our limited ability to observe the processes involved in real-time. ...
Initially a matter of intellectual curiosity, but now important for understanding ice‐sheet dynamics, the formation of subglacial bedforms has been a subject of scientific enquiry for over a century. Here, we use a numerical model of the coupled flow of ice, water, and subglacial sediment to explore the formation of subglacial ribs (i.e. ribbed moraine), drumlins and mega‐scale glacial lineations (MSGL). The model produces instabilities at the ice‐bed interface, which result in landforms resembling subglacial ribs and drumlins. We find that a behavioural trajectory is present. Initially subglacial ribs form, which can either develop into fields of organised drumlins, or herringbone‐type structures misaligned with ice flow. We present potential examples of these misaligned bedforms in deglaciated landscapes, the presence of which means caution should be taken when interpreting cross‐cutting bedforms to reconstruct ice flow directions. Under unvarying ice flow parameters, MSGL failed to appear in our experiments. However, drumlin fields can elongate into MSGL in our model if low ice‐bed coupling conditions are imposed. The conditions under which drumlins elongate into MSGL are analogous to those found beneath contemporary ice streams, providing the first mechanism, rather than just an association, for linking MSGL with ice stream flow. We conclude that the instability theory, as realised in this numerical model, is sufficient to explain the fundamental mechanics and process‐interactions that lead to the initiation of subglacial bedforms, the development of the distinctive types of bedform patterns, and their evolutionary trajectories. We therefore suggest that the first part of the longstanding ‘drumlin problem’ – how and why they come into existence ‐ is now solved. However, much remains to be discovered regarding the exact sedimentary and hydrological processes involved.
... However, we acknowledge that our data are spatially limited within the Bustarfell drumlin field and stress that this inference could be tested with more extensive excavations and GPR profiling across the field. Dowling (2016) demonstrated that pre-existing obstacles, which could serve as drumlin cores, are necessary for the initiation of drumlin formation in areas characterised by thin glacial drift and where bedrock knobs are lacking. If obstacles like glaciofluvial outwash exist, then drumlin formation is initiated through differential flow over and around them (Boulton, 1987). ...
Drumlins are important bedforms of former glaciated landscapes as they demonstrate past ice‐flow directions and elucidate processes that operated at the ice/bed interface. Recently mapped drumlins and other streamlined subglacial bedforms in northeast Iceland reveal the flow‐sets of cross‐cutting palaeo‐ice streams that were active within the Iceland Ice Sheet (IIS) during and following the Last Glacial Maximum. Here we study the Bustarfell drumlin field within the Vopnafjörður–Jökuldalsheiði flow‐set. The internal architecture of two drumlins was investigated using sedimentological analysis and ground‐penetrating radar (GPR, 50 and 100 MHz) to illuminate subglacial processes that contributed to drumlin formation, as well as the history and dynamics of the IIS. On the stoss side of one of the drumlins, two subglacial traction till units were identified, separated by a thick unit of deformed glaciofluvial sand and gravel. The core of glaciofluvial material suggests that the drumlin formed around well‐drained patches (sticky spots) in the subglacial bed that retarded the ice flow locally through increased basal drag and encouraged till deposition. Furthermore, our GPR data indicate a combination of erosional and depositional processes. We suggest that the glaciofluvial sediments were deposited as small ice‐marginal fans on the Bustarfell plateau, possibly during the Bølling–Allerød interstadial, and that the drumlins were formed around these fans during a subsequent readvance during the Younger Dryas.
... The word "drumlinization" refers to the remolding of pre-existing sediments and rock forms (Benn and Evans, 2014). The term "drumlinoid" or "drumlinoidal feature" is also often used in literature defined by the break of slope compared to the base of the landform feature, length, width, height and elongation ratio (Dowling, 2016). ...
... During the glacial retreat of the Scandinavian ice sheet, the drumlins of Latvia formed predominantly by the Zemgale ice lobe (Lamsters, 2012). Drumlins are also documented from Sweden, Great Britain, Ireland, and Iceland (Benn and Evans, 2014, Dowling, 2016, Dowling et al., 2016, McCracken et al., 2016, Putkinen et al., 2017, which fuel the drumlin theory in NE Germany. ...
... During the glacial retreat of the Scandinavian ice sheet, the drumlins of Latvia formed predominantly by the Zemgale ice lobe (Lamsters, 2012). Drumlins are also documented from Sweden, Great Britain, Ireland, and Iceland (Benn and Evans, 2014, Dowling, 2016, Dowling et al., 2016, McCracken et al., 2016, Putkinen et al., 2017, which fuel the drumlin theory in NE Germany. ...
Although evidence shows different phases of the Weichselian glaciation in Mecklenburg Western Pommerania, there remains a vast scope of the glacial study. Since drumlins hold significant clues regarding glacier flow direction and behavior, this study targeted two sites (A and B) to prove as drumlins. The main objectives were to explore the sediment accumulations, distribution and present an argument on the drumlin hypothesis. The digital elevation model (1 m resolution) of the study area was collected from the Landesamt für innere Verwaltung Mecklenburg-Vorpommern (LAiV M-V), and topography, geomorphology, morphology and morphometric characteristics were analyzed using ArcGIS and Microsoft Excel. Primary geophysical data and photos were collected from the field and examined using ReflexW (version 7.5) software. 100 MHz shielded antenna and 185 ns time window were used for the GPR analysis. The topographical, geomorphological, and morphological maps suggest that the origin and formation of the two sites are different. While both sites have some drumlin characteristics (e.g., height, width, and slope angle), the geographic position and characteristics of meltwater deposition found in those areas are different from each other. Due to saturated soil, the GPR method did not provide interpretable information regarding the stratigraphic layers. Because of pore water in the soil, attenuation increased; consequently, penetration decreased. This study argues that site-A is a drumlin, drumlinoid or drumlinoidal feature. Deformation of eskers by active glacier movement caused this formation. On the other hand, the chaotic meltwater deposits and their characteristics indicate site-B is a supraglacial hummocky moraine. However, the landforms are more complex than a definitive conclusion. ii Acknowledgment I want to express my deepest gratitude to everyone who supported make this work possible.
... Drumlin shapes and sizes may be modulated by the hydrogeological properties of the material (Piotrowski, 1987;Rattas and Piotrowski, 2003;Dowling, 2015;McCracken et al., 2016;Iverson et al., 2017) and the strength of coupling between the ice and its bed (e.g. Engelhardt and Kamb, 1998;Breemer et al., 2002;Clarke, 2005;Lesemann et al., 2010a). ...
Drumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high‐resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo‐ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600‐800 m long, 200‐250 m wide, 3‐6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down‐slope and where thick fine‐grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up‐slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre‐date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes.
... A combination of slope analysis and visual inspection was used to delimit the drumlins at a break in slope, which could either be abrupt (e.g., lakes, outwash) or gradual. Only where both axes of a putative drumlin (long, short) were upstanding from the landscape was the planform shape considered delineated and a drumlin defined (Dowling 2016). However, if small forms have similar morphology to their larger companions, this will not impact the size-frequency distribution of drumlins (see Section 6.1). ...
... Moreover, even applying a conservative correction for under-sampling during manual mapping is equally insufficient to invalidate the result (Section 4.3). Some doubt might exist as a conservative mapping method was used Dowling 2016), requiring each drumlin to be elevated above its surroundings on all sides. This could miss subtle drumlins that are low relief, but wide and long, because if they are on a gentle larger scale (i.e., "regional" [see Hillier & Smith 2008]) slope, then the up-dip face of the drumlin may only be shallower and never actually slope downward. ...
Few very small drumlins are typically mapped in previously glaciated landscapes, which might be an important signature of subglacial processes or an observational artefact. One hundred and forty-three newly emergent drumlins, recently sculpted by the Múlajökull glacier, have been mapped using high-resolution LiDAR and aerial photographs in addition to field surveying. In this paper, these are used as evidence that few small drumlins (e.g., height H ≲ 4 m, width W ≲ 40 m, length L ≲ 100 m) are produced; at least, few survive to pass outside the ice margin in this actively forming drumlin field. Specifically, the lack of a multitude of small features seen in other landforms (e.g., volcanoes) is argued not to be due to (i) Digital Elevation Model resolution or quality, (ii) mapper ability in complex (i.e., anthropogenically cluttered or vegetated) landscapes or (iii) post-glacial degradation at this site. So, whilst detection ability must still be at least acknowledged in drumlin mapping, and ideally corrected for in quantitative analyses, this observation can now be firmly taken as a constraint upon drumlin formation models (i.e., statistical, conceptual or numerical ice flow). Our preferred explanation for the scarcity of small drumlins, at least at sites similar to Múlajökull (i.e., ice lobes with near-margin drumlin genesis), is that they form stochastically during multiple surge cycles, evolving from wide and gentle pre-existing undulations by increasing rapidly in amplitude before significant streamlining occurs.
... Drumlins are observed both in marine and terrestrial settings, and their origin has challenged glacial geologists for decades (Wright Jr 1957;Menzies & Rose 1987;Fader et al. 1997;Benn & Evans 2010). The quest for a unifying theory of drumlin formation, composition and shape has been one strong focus of drumlin research, and has resulted in numerous publications of varying conceptual and theoretical models for drumlin formation (e.g., Smalley & Unwin 1968;Shaw 1983;Boulton 1987;Menzies & Rose 1987;Hart 1997;Stokes et al. 2011;Spagnolo et al. 2012;Dowling 2016;Iverson et al. 2017). The morphology of a drumlin is classically described as a smooth, oval, half egg-shaped hill with a blunt stoss side and a tapering lee side (Menzies 1979). ...
... Clark et al. (2009) argued that drumlin shape varies considerably and their size is not strictly defined. Consequently, it can be argued that drumlins often show equifinality and their end state can be reached by many potential means (Menzies & Rose, 1987;Dowling 2016). The term drumlin has been applied to a wide range of bedforms with different morphologies and composition, and the development of a unifying theory of formation thus seems unlikely (Goudie 2004;Dowling 2016). ...
... Consequently, it can be argued that drumlins often show equifinality and their end state can be reached by many potential means (Menzies & Rose, 1987;Dowling 2016). The term drumlin has been applied to a wide range of bedforms with different morphologies and composition, and the development of a unifying theory of formation thus seems unlikely (Goudie 2004;Dowling 2016). ...
The study of glacial landforms is important for understanding past subglacial processes and dynamics. The Nordenskiöldbreen forefield hosts numerous streamlined landforms resulting from a late Holocene glacier advance. Here, we present a geomorphological map constructed from remotely sensed imagery of both the marine and terrestrial environments. Sixteen drumlin bedforms have been identified in the mapped forefield – ten terrestrial and six submarine. A sedimentological investigation of drumlins in the Nordenskiöldbreen forefield shows that they are composed of pre-existing sediments draped by a thin layer of till which formed during the most recent advance of the glacier. Analysis of recent (2008–2012), high-resolution aerial imagery of all the glacier forelands in Svalbard suggests drumlin features are widespread. Here, we have identified 49 previously undocumented terrestrial glacier forefields, where subglacially streamlined landforms occur within the margins of the late Holocene glacier extent. Additionally, the location of 53 previously published submarine sites with streamlined landscape have been mapped. Thirty of these are sites with streamlines of late Holocene origin and 18 with Last Glacial Maximum (LGM) origin. Based on our detailed case study at the Nordenskiöldbreen forefield, and remote sensing survey, we suggest that drumlins in Svalbard form predominantly in forefields of glaciers with low-elevation termini, in areas with abundant fine-grained sediments, and where the glaciers are able to advance into an area of unconstrained topography.
... As the metric's distributions are found to be log-normal, the values are log-normalised before they are plotted against one another in order to enable robust conclusions, particularly when moving to three-variable plotting . Morphological values for streamlined terrain mentioned in this paper, and how these were derived, are described in , 2016. ...
... We have recently published a number of papers dealing with drumlin morphology, internal composition and possible origin in a regional context for southern Sweden (Dowling 2016;Dowling et al. 2015Dowling et al. , 2016Möller & Murray 2015;, 2016. We reference these papers for more in-depth descriptions and interpretations, and here review the main conclusions on the types of drumlins typical for the glacial landscape of south Sweden and how streamlined terrain relates -or not -to ribbed moraine. ...
... We have recently published a number of papers dealing with drumlin morphology, internal composition and possible origin in a regional context for southern Sweden (Dowling 2016;Dowling et al. 2015Dowling et al. , 2016Möller & Murray 2015;, 2016. We reference these papers for more in-depth descriptions and interpretations, and here review the main conclusions on the types of drumlins typical for the glacial landscape of south Sweden and how streamlined terrain relates -or not -to ribbed moraine. ...
A contemporary trend in glacial geomorphology is the quest for a unifying theory of drumlin and ribbed moraine formation. Three Swedish example areas of each are here newly mapped, using high-resolution Light Detecting and Ranging (LiDAR) data. From previous ribbed moraine studies in these areas, we know that they formed differently, one by melt-out of stagnant debris-zonated ice, another by remoulding of pre-existing landforms and the third by active subglacial stacking and folding of sediment into proto ridges, contemporaneously with lee-side cavity sediment infill. Through previous work on streamlined terrain in Sweden we know that rock-cored drumlins dominate, while soft-cored drumlins are much less common. The morphology of both types varies along a continuum, whereas their processes of formation differ. Our field examples from ribbed moraine tracts and streamlined terrain suggest that the subglacial environment contains a suite of different ice-sediment physics that, irrespective of this, leads to an equifinality of shape of some subglacial landforms (ribbed moraine and streamlined terrain) despite the differences in the detail of their process of formation. We thus argue that different processes, on their own or in combination, lead to a similar form of morphometric expression, that is, equifinality, and the quest for a unifying process of formation is a misleading one. Furthermore, we argue that large morphological data-sets of subglacial landforms can only be used to classify features as part of a formation continuum-or not-when they are used in conjunction with the sedimentology of said landforms.
... Elsewhere, the break in slope is subtle so that the drumlins could only be delimited with significant vertical exaggeration of the hillshade and ground-checking in the field. Drumlins were only defined where both drumlin axes were upstanding from the landscape so that the planform shape of the drumlins could be delineated (Dowling 2016). Thus, other drumlinoid or streamlined features in the forefield are not included in the mapping, which consequently can be considered as conservative. ...
The drumlin field at Múlajökull, Iceland, is considered to be an active field in that partly and fully ice-covered drumlins are being shaped by the current glacier regime. We test the hypothesis that the drumlins form by a combination of erosion and deposition during successive surge cycles. We mapped and measured 143 drumlins and studied their stratigraphy in four exposures. All exposures reveal several till units where the youngest till commonly truncates older tills on the drumlin flanks and proximal slope. Drumlins inside a 1992 moraine are relatively long and narrow whereas drumlins outside the moraine are wider and shorter. A conceptual model suggests that radial crevasses create spatial heterogeneity in normal stress on the bed so that deposition is favoured beneath crevasses and erosion in adjacent areas. Consequently, the crevasse pattern of the glacier controls the location of proto-drumlins. A feedback mechanism leads to continued crevassing and increased sedimentation at the location of the proto-drumlins. The drumlin relief and elongation ratio increases as the glacier erodes the sides and drapes a new till over the landform through successive surges. Our observations of this only known active drumlin field may have implications for the formation and morphological evolution of Pleistocene drumlin fields with similar composition, and our model may be tested on modern drumlins that may become exposed upon future ice retreat.
... Self-organizing maps (Kohonen, 2001) have been highlighted as a valuable technique for analyzing subtle relationships between disparate data sets (Fraser and Dickson, 2007). Although traditionally developed for finance, an increasing number of geoscience studies are using self-organizing maps, for example, to explore the relationship between streamlined glacial bedforms and the geological setting of the features (Dowling, 2016). ...
Using the LiDAR-derived Swedish national height model we have identified previously undescribed shallow streamlined glacial bedforms, small-scale drumlins, on the Närke plain in south-central Sweden. These drumlins could only be detected with high-resolution LiDAR, due to both their subtle size and forest cover. In this area the ice margin receded in a subaqueous environment with a proglacial water depth in the order of 100 m during the last deglaciation. As indicated by the configuration of marginally formed De Geer moraine ridges draping the drumlinoids, the receding ice margin formed deeply indented calving bays. These were located around subaqueous outlets of the subglacial melt-water drainage, with their apex position marked geomorphologically by beaded esker ridges. The mapped small-scale drumlins are aligned perpendicular to the reconstructed ice sheet margin and suggest formation along flow lines adjusted to the configuration of these calving embayments as they propagated up-flow with ice margin retreat. Based on these geometric relationships we argue that the emplacement of the drumlins was near-marginal, ∼7.7–1 km from the margin, on a short timescale (∼5–35 years).
